1. Field of the Invention
The present invention relates to a projection-type display device which can be applied to for example a projector device for projecting an optical image spatially modulated by reflection-type liquid crystal panels onto a screen.
2. Description of the Related Art
In the related art, a projection-type display device has been proposed which is configured to use reflection-type liquid crystal panels to generate spatially modulated optical images and to project the optical images onto a screen so as to form a desired color image.
Among such projection-type display devices, ones have been proposed which use dichroic mirrors or use dichroic prisms as the means for breaking down illumination light obtained from a light source into red, blue, and green illumination light for supply to corresponding reflection-type liquid crystal panels and for synthesizing the red, green, and blue optical images obtained from the reflection-type liquid crystal panels.
FIG. 1 is a view of the configuration of a projection-type display device using dichroic prisms.
In this projection-type display device 1 using dichroic prisms, as shown in FIG. 1, a light source 2 is comprised for example a discharge lamp 3 and a reflector 4 and emits white illumination light.
Further, the light source 2 uses fly eye lenses 5A and 5B to make the distribution of the amount of the illumination light uniform, then emits the light to a plane polarization conversion element 6. Here, the plane polarization conversion element 6 selectively transmits mainly the s-polarization component and converts the p-polarization component orthogonal to this to the s-polarization component.
Due to this, the light source 2 emits illumination light increased in the polarization component effective for the image display in the illumination light projected from the discharge lamp 3 by the various plane polarizations and reduced in the polarization component orthogonal to this. As a result, the efficiency of utilization of the illumination light is improved by that extent and the contrast of the display image is improved.
A convex lens 7 converges and emits this illumination light on the path of the illumination light emitted from the plane polarization conversion element 6.
A cold mirror 8 emits the components of the illumination light emitted from the convex lens 7 other than the infrared region reflected in a direction 90 degrees from the path of incidence.
A convex lens 9 converges and emits the illumination light reflected at the cold mirror 8.
A polarization beam splitter 11 is formed by adhering inclined planes of rectangular prisms to each other and is formed with a detecting plane 11A at the adhered planes. The polarization beam splitter 11 selectively reflects and emits from the detecting plane 11A the illumination light due to the s-polarized light emitted from the convex lens 28, while selectively transmits the p-polarization component in the synthesized optical image incident on it traveling back along the path of the illumination light due to the s-polarized light and returns the s-polarization component to the light source 2.
A dichroic prism 12 is formed by adhering inclined planes of three prisms each having a predetermined form to each other and is arranged so that the adhered planes cut across the path of the light projected from the polarization beam splitter 11. The dichroic prism 12 is formed with dichroic films MB, MR obtained by lamination of dielectric films to a predetermined thickness on the adhered planes cutting across the optical path. The blue and red illumination light in the illumination light projected from the polarization beam splitter 11 are successively selectively reflected at the dichroic films MB, MR. Due to this, the dichroic prism 12 breaks down the illumination light projected from the polarization beam splitter 11 into blue, red, and green illumination light and supplies them to the blue, red, and green color reflection-type liquid crystal panels 13B, 13R, and 13G arranged at the bottom surface of the prism.
The reflection-type liquid crystal panels 13B, 13R, and 13G are driven by corresponding color signals. The illumination light incident by the s-polarized light is reflected with the plane polarization rotated for every pixel. Due to this, optical images changed in plane polarization in accordance with the color signals are projected.
The dichroic prism 12, conversely to the case of the illumination light, synthesizes the blue, red, and green optical images obtained from the reflection-type liquid crystal panels to generate a synthesized optical image and projects the synthesized optical image to the polarization beam splitter 11.
Specifically, the synthesized optical image travels back along the path of the illumination light due to the synthesized light of the p-polarized light and s-polarized light in accordance with the color signals and is emitted to the polarization beam splitter 11. Further, only the p-polarization component in the synthesized optical image passes through the polarization beam splitter 11 and is projected to the projection lens 14.
In this way, the projection lens 14 projects the synthesized optical image passing through the polarization beam splitter 11 to the screen 15. Due to this, a color image is displayed by enlarging and projecting onto the screen the images generated by the reflection-type liquid crystal panels 13B, 13R, and 13G.
Further, a projection-type display device using dichroic mirrors is configured to break down the illumination light incident from a polarization beam splitter into red, blue, and green illumination light by dichroic mirrors instead of the dichroic prisms 12 and project them onto the reflection-type liquid crystal panels and to synthesize the optical images projected from the reflection-type liquid crystal panels and emit the result on a projection lens.
In this type of projection-type display device 1, however, there has been the disadvantage that the so-called haze phenomenon occurs where light is also projected at portions which should inherently be displayed black and those portions are displayed whitish and this haze phenomenon causes a reduction in the contrast of the projected image.
The haze phenomenon will be explained in further detail below.
In the projection-type display device 1, the portion which inherently should be displayed black is reflected without any rotation of the plane polarization of the corresponding illumination light at the reflection-type liquid crystal panels. As a result, in the projection-type display device 1, the corresponding optical images are returned to the light source 2 side by the polarization beam splitter 11. Due to this, the corresponding portion should be displayed black on the screen 15.
In the projection-type display device 1, however, this type of optical image which should be detected at the polarization beam splitter 11 by the s-polarized light is detected by the synthesized light of the s-polarized light and the p-polarized light. Due to this, this type of haze phenomenon is generated.
That is, in an optical system provided with a polarization beam splitter 11, dichroic prisms 12, etc., a phase difference is given in the direction of vibration of the light to the p-polarized light parallel to the boundary planes and the s-polarized light orthogonal to the p-polarization component using as a reference the incidence plane and emission plane of the polarization beam splitter 11, the light detecting plane, the boundary plane of the dichroic film etc. Due to this, in this type of projection-type display device, when viewed as an optical system as a whole, the direction of the p-polarization component initially separated by the polarization beam splitter 11 changes at the boundary planes. Further, the phase difference generated at the boundary planes in this way changes by the incident wavelength and angle of incidence to the boundary planes.
As a result, in the projection-type display device 1, the states of polarization change in the illumination light and optical images propagated through the optical system. Due to this, light is mixed into the portions inherently to be displayed black by the s-polarized light and the haze phenomenon occurs.
FIG. 2 is a view for explaining the changes in the states of polarization. FIG. 2 corresponds to the configuration of the above-mentioned FIG. 1 and shows the case where the illumination light incident from the convex lens 9 is reflected at the polarization beam splitter 11, then successively passes through the dichroic films MB, MR, and strikes the reflection-type liquid crystal panel 13G where it is reflected without modulation. Note that below the letter B will be added to the references to indicate a vector.
In this case, assume that the unit vector showing the direction of the incident illumination light is the direction cosine BC0 and the direction cosines showing the directions of the illumination light at the boundary planes of the detecting plane 11A of the polarization beam splitter 11 and the dichroic film MB and dichroic film MR, all boundary planes, are BC1, BC2, and BC3. Further, the direction cosines showing the directions of the optical images at the corresponding boundary planes after reflection by the reflection-type liquid crystal panels 13G are BC4, BC5, and BC6. Further, the unit vectors showing the arrangement of the boundary planes corresponding to these direction cosines are made normal vectors and indicated by the references BD1, BD2, BD3, BD4, BD5, and BD6.
The s-polarization components BESn orthogonal to the incidence planes of the boundary planes are defined by the following equation with the direction of advance defined by the outer product of the direction cosines and the normal vectors:
BESn=BCnxc3x97BDn/|BCnxc3x97BDn|xe2x80x83xe2x80x83(1)
(where, n=1 to 6)
Further, the direction cosines of the p-polarization component parallel to the incidence planes of the boundary planes intersect the direction of advance of the s-polarization components BESn at right angles and are expressed by the vector products of the following equation:
BEPn=BESnxc3x97BCn/|BESnxc3x97BCn|xe2x80x83xe2x80x83(2)
(where, n=1 to 6)
At this time, the direction cosines become BC2=BC3xe2x89xa0BC1, BC4=BC5xe2x89xa0BC6. Due to the refraction at the polarization beam splitter 11, only the direction cosines BC1 and BC6 differ. Note that the normal vectors are BD1≈BD2, inner product BD2xc2x7BD3≈0, BD5≈BD6, inner product BD4xc2x7BD5≈0.
It is possible to obtain the relationship of the following formula from formula (1), formula (2), and the relationship of the direction cosine BCn and the normal vector BDn. Note that the orthogonal p-polarization component BEPn becomes the same relationship.
BES1≈BES2xe2x89xa0BES3xe2x80x83xe2x80x83(3)
FIGS. 3A to 3J are views of the states of polarization around the boundary planes by the absolute coordinate system x-y seen from the reflection-type liquid crystal panel side.
As shown in FIG. 3A, at the reflection side of the detecting plane 11A of the polarization beam splitter 11, the illumination light due to the direction cosine BC0 strikes the polarization beam splitter 11. Only the s-polarization component is selectively reflected in accordance with the direction of the p-polarization component and the s-polarization component determined at the detecting plane 11A and becomes linear polarized light.
As opposed to this, in front of the boundary plane of the dichroic film MB, as shown in FIG. 3B, the directions of the p-polarization component and s-polarization component differ slightly from the time of reflection at the polarization beam splitter 11 (the p-polarization component and s-polarization component at the dichroic film shown by the broken line rectangle). Due to this, the illumination light is broken down into the p-polarization component and the s-polarization component at the dichroic film MB and given a phase difference (BES1≈BES2).
As a result, after the boundary plane of the dichroic film MB, as shown in FIG. 3C, the illumination light becomes elliptical polarized light.
Further, in front of the boundary plane of the dichroic film MR, as shown in FIG. 3D, the directions of the p-polarization component and s-polarization component largely differ. The illumination light is broken down at the dichroic film MR into the p-polarization component and s-polarization component which are then given a phase difference (BES2xe2x89xa0BES3).
As a result, as shown in FIG. 3E, after the boundary plane of the dichroic film MR, the illumination light can become elliptical polarized light with a largely increased short diameter. When reflected without any polarization at the reflection-type liquid crystal panel 13G, the reflected light becomes elliptical polarized light as showing the front of the boundary plane of the dichroic film MR in FIG. 3F.
The optical image projected from the reflection-type liquid crystal panel as the elliptical polarized light in this way, as shown in FIGS. 3F to 3I, in the same way as the illumination light, is successively broken down into the corresponding p-polarization component and s-polarization component by the dichroic films MR, MB. As shown in FIG. 3J, when striking the detecting plane 11A of the polarization beam splitter 11, an s-polarization component is generated with respect to the detecting plane 11A as shown by the broken rectangle showing the directions of the p-polarized light and s-polarized light at the detecting plane 11A. In this case, the larger the amount of the p-polarization component BEPn, the greater the amount of light leaking out to the projection lens 14 and the more a haze state is formed.
As one method to solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 6-175123 proposes the method of arranging the dichroic film inclined in the opposite direction with respect to the detecting plane 11A of the polarization beam splitter 11 and designing a dielectric multilayer film comprising the dichroic film so as to reduce the change in the state of polarization.
In this first method, the phase difference given to the p-polarization component and s-polarization component by the dichroic films at the boundary plane changes depending on the incident wavelength and angle of incidence. Therefore, it is possible to form a state sufficiently satisfying the change in the state of polarization for a specific wavelength and specific angle of incidence.
In the first method, however, it is difficult to obtain a satisfactory state for an incident wavelength and angle of incidence different from the specific wavelength and specific angle of incidence. In the final analysis, there are still problems in practice.
Further, Japanese Unexamined Patent Publication (Kokai) No. 10-26756, as shown in FIG. 4, proposes a second method of arranging the detecting plane 11A and dichroic films MB, MR in parallel and providing a quarter wavelength plate xcex/4 in front of the reflection-type liquid crystal panel 13G so as to reduce the haze phenomenon.
In this case, among the direction cosines, only the direction cosines BC1 and BC6 differ due to the refraction of the polarization beam splitter 11, so BC2=BC3xe2x89xa0BC1 and BC4=BC5xe2x89xa0BC6. Further, the normal vectors become BD1≈BD2≈BD3 and BD4≈BD5≈BD6.
In this case, the relationship of the following formula is obtained from formulas (1) and (2) and the relationship between the direction cosines BCn and the normal vectors BDn. Note that the orthogonal p-polarization component BEPn becomes the same relationship.
BES1≈BES2≈BES3xe2x80x83xe2x80x83(4)
As shown by the state of polarization in the case of application of the second method in FIGS. 5A to 5J from the comparison with FIGS. 3A to 3J, according to the second method, by arranging the detecting plane 11A and the dichroic films MB, MR, it is possible to make the p-polarization component and the s-polarization component substantially match (BES1≈BES2≈BES3) just before the detecting plane 11A (FIG. 5A), just before the dichroic film MB (FIG. 5B), and just before the dichroic film MR (FIG. 5D) and to reduce changes in the state of polarization.
Further, by arranging a quarter wavelength plate xcex/4 with a retardation phase axis matched with the Y-axis, it is possible to make the optical image (FIG. 5F) emitted from the quarter wavelength plate xcex/4 symmetrical with the Y-axis of the illumination light (FIG. 5E) incident on the quarter wavelength plate xcex/4. Therefore, it is possible to make the p-polarization component and the s-polarization component substantially match just before the dichroic film MR at the optical image (FIG. 5F), just before the dichroic film MB (FIG. 5H), and just before the detecting plane 11A (FIG. 5J) and possible to reduce the p-component (BEP6) incident on the detecting plane 11A.
However, considering the dependence of a quarter wavelength plate xcex/4 on the angle of incidence and wavelength, when in the case of an index of refraction of the extraordinary ray Ne, the index of refraction of the ordinary ray No, and the thickness D, a phase difference is given to the planes of vibration by exactly a retardation shown in the following formula in the quarter wavelength plate xcex/4, where, xcex94N=Ne-No, xcex= incident wavelength, and xcex8= angle of incidence:                     σ        =                              2            ⁢            πΔ            ⁢                          xe2x80x83                        ⁢            ND                                λ            ⁢                          xe2x80x83                        ⁢            COS            ⁢                          xe2x80x83                        ⁢            θ                                              (        5        )            
The quarter wavelength plate xcex/4 is a phase difference plate with a xcex94ND of xcex0/4 with respect to an angle of incidence xcex8 of 0 and a specific wavelength of xcex0. The phase difference given to the p-polarized light and the s-polarized light changes in accordance with the incident wavelength and angle of incidence on the path of the illumination light.
On this point, in the example explained in relation to FIGS. 5A to 5J, the phase differences given to the planes of vibration by the dichroic films MB, MR also change according to the incident wavelength and the angle of incidence. Due to this, depending on the quarter wavelength plate xcex/4, when the directions of the p-polarization component and the s-polarization component differ even slightly, the light emitted from the detecting plane 11A due to linear polarization changes to elliptical polarized light depending on the angle of incidence and wavelength of the illumination light. In the end, at the stage where the optical image strikes the detecting plane 11A, it is no longer possible to sufficiently reduce the p-polarization component (BEP6) at the detecting plane 11A.
Further, even when the detecting plane 11A and dichroic films MB, MR are arranged in parallel, in practice the illumination light incident on and emitted from the polarization beam splitter 11 is light with a spread. The direction cosine changes due to the index of refraction of the polarization beam splitter 11 and the angle of incidence of the illumination light to the dichroic films MB, MR becomes larger.
Due to this, the illumination light shown in FIG. 5B incident on the dichroic film MB becomes elliptical polarized light. Further, when passing back and forth through the quarter phase plate xcex/4, it is given a phase difference of at least 90 degrees according to the above formula (5). Due to this, in the illumination light, a state of non-symmetry about the Y-axis is formed between the case when emitted from the dichroic film MR toward the reflection-type liquid crystal panel 13G (FIG. 5E) and the case when reflected at the reflection-type liquid crystal panel 13G by non-polarization and striking the dichroic film MR.
In this case, when the optical image repeatedly passes through the dichroic films MR, MB and strikes the detecting plane 11A of the polarization beam splitter 11, it is difficult to make the p-component (BEP6) of the polarization beam splitter 11 the smallest and the p-component of the elliptical polarized light is emitted to the projection lens 14.
Due to these, it is difficult even with the second method to sufficiently reduce the haze phenomenon and increase the contrast of the display image.
An object of the present invention is to provide a projection-type display device able to prevent a reduction in contrast due to the haze phenomenon and display a high quality display image and a method of adjustment of the same.
According to a first aspect of the present invention, there is provided a projection-type display device provided with at least a plurality of reflection-type image forming means for spatially modulating and reflecting incident light and emitting optical images rotated in plane polarization with respect to a plane polarization of the incident light; a light source for emitting illumination light; color separating and synthesizing means for breaking down the illumination light by wavelengths corresponding to the reflection-type imaging forming means and outputting the results to the reflection-type image forming means and for synthesizing optical images obtained from the reflection-type image forming means and emitting the synthesized optical image; a projection optical system for projecting the synthesized optical image to a predetermined projection object; and a polarization beam splitter for emitting a predetermined plane polarization component from the illumination light emitted from the light source to the color separating and synthesizing means and emitting the synthesized optical image obtained from the color separating and synthesizing means to the projection optical system; phase difference plates being arranged facing the light incidence/emission planes of the reflection-type image forming means; the phase difference plates setting retardations for canceling out the retardation comprised of the retardation corresponding to one-quarter of the wavelength of the incident light due to the polarization beam splitter plus retardation due to the color separating and synthesizing means.
According to a second aspect of the present invention, there is provided a projection-type display device provided with at least a plurality of reflection-type image forming means for spatially modulating and reflecting incident light and emitting optical images rotated in plane polarization with respect to a plane polarization of the incident light; a light source for emitting illumination light; color separating and synthesizing means for breaking down the illumination light by wavelengths corresponding to the reflection-type imaging forming means and outputting the results to the reflection-type image forming means and for synthesizing optical images obtained from the reflection-type image forming means and emitting the synthesized optical image; a projection optical system for projecting the synthesized optical image to a predetermined projection object; and a polarization beam splitter for emitting a predetermined plane polarization component from the illumination light emitted from the light source to the color separating and synthesizing means and emitting the synthesized optical image obtained from the color separating and synthesizing means to the projection optical system; phase difference plates being arranged facing the light incidence/emission planes of the reflection-type image forming means; the retardations at the phase difference plates being set based on results of the ray tracing from the polarization beam splitter to the reflection-type image forming means, changing in accordance with the characteristics of the color separating and synthesizing means with respect to the angle of incidence and wavelength.
In the present invention, in the case of changing the retardations of the phase difference plates in various ways, the retardations of the phase difference plates are set to retardations giving the smallest overall amount of light passing through the polarization beam splitter in the case of a black level based on the ray tracing for each wavelength and angle of incidence of the illumination light incident from the polarization beam splitter to the color separating and synthesizing means.
Preferably, the color separating and synthesizing means comprises at least one dichroic mirror.
Preferably, the color separating and synthesizing means comprises at least one dichroic prism.
According to a third aspect of the present invention, there is provided a projection-type display device provided with at least a plurality of reflection-type image forming means for spatially modulating and reflecting incident light and emitting optical images rotated in plane polarization with respect to a plane polarization of the incident light; a light source for emitting illumination light; color separating and synthesizing means for breaking down the illumination light by wavelengths corresponding to the reflection-type imaging forming means and outputting the results to the reflection-type image forming means and for synthesizing optical images obtained from the reflection-type image forming means and emitting the synthesized optical image; a projection optical system for projecting the synthesized optical image to a predetermined projection object; and a polarization beam splitter for emitting a predetermined plane polarization component from the illumination light emitted from the light source to the color separating and synthesizing means and emitting the synthesized optical image obtained from the color separating and synthesizing means to the projection optical system; phase difference plates being arranged facing the light incidence/emission planes of the reflection-type image forming means; the phase difference plates changing the directions of polarization of the optical images in planes substantially orthogonal to the optical axis and being adjusted to positions making the direction of polarization of a detecting plane of the polarization beam splitter and the directions of polarization of the optical images substantially match.
According to a fourth aspect of the invention, there is provided projection-type display device provided with at least a plurality of reflection-type image forming means for spatially modulating and reflecting incident light and emitting optical images rotated in plane polarization with respect to a plane polarization of the incident light; a light source for emitting illumination light; color separating and synthesizing means for breaking down the illumination light by wavelengths corresponding to the reflection-type imaging forming means and outputting the results to the reflection-type image forming means and for synthesizing optical images obtained from the reflection-type image forming means and emitting the synthesized optical image; a projection optical system for projecting the synthesized optical image to a predetermined projection object; and a polarization beam splitter for emitting a predetermined plane polarization component from the illumination light emitted from the light source to the color separating and synthesizing means and emitting the synthesized optical image obtained from the color separating and synthesizing means to the projection optical system; phase difference plates being arranged facing the light incidence/emission planes of the reflection-type image forming means; holding mechanisms for holding the phase difference plates rotatably in planes substantially orthogonal to the optical axes being provided.
In the present invention, preferably, the phase difference plates set retardations so as to cancel out retardation comprised of the retardation corresponding to one-quarter of the wavelength of the incident light from the polarization beam splitter plus the retardations due to the color separating and synthesizing means.
Further, in the present invention, retardations at the phase difference plates are set based on results of the ray tracing from the polarization beam splitter to the reflection-type image forming means, changing in accordance with the characteristics of the color separating and synthesizing means with respect to the angle of incidence and wavelength.
Further, preferably, in the case of changing the retardations of the phase difference plates in various ways, the retardations of the phase difference plates are set to retardations giving the smallest overall amount of light passing through the polarization beam splitter in the case of a black level based on the ray tracing for each wavelength and angle of incidence of the illumination light incident from the polarization beam splitter to the color separating and synthesizing means.
Further, in the present invention, preferably the inclinations of the color separating and synthesizing means are set so that the angles between the optical axes of the illumination light on the color separating and synthesizing means and the optical axes of the optical images become smaller than 90 degrees.
According to a fifth aspect of the invention, there is provided a method of adjustment of a projection-type display device provided with at least a plurality of reflection-type image forming means for spatially modulating and reflecting incident light and emitting optical images rotated in plane polarization with respect to a plane polarization of the incident light; color separating and synthesizing means for breaking down the illumination light by wavelengths corresponding to the reflection-type imaging forming means and outputting the results to the reflection-type image forming means and for synthesizing optical images obtained from the reflection-type image forming means and emitting the synthesized optical image; and a polarization beam splitter for emitting a predetermined plane polarization component from the illumination light emitted from a light source to the color separating and synthesizing means and emitting the synthesized optical image obtained from the color separating and synthesizing means to a projection optical system; wherein phase difference plates are made to rotate in planes substantially orthogonal to the optical axes to adjust the phase differences given to the incident light and the optical images.
In the present invention, the phase difference plates are made to rotate in planes substantially orthogonal to the optical axes to change the directions of polarization of the optical images and wherein the positions of arrangement of the phase difference plates are adjusted to positions where the direction of polarization of the detecting plane of the polarization beam splitter and the directions of polarization of the optical images substantially match so as to adjust the phase differences given to the incident light and the optical images.
Further, preferably, after the adjustment ends, the phase difference plates are secured to the adjusted positions.
According to the first and second aspects of the present invention, by setting the retardations in the phase difference plates doubly refracting the incident light and the optical images so as to cancel out the retardation comprised of the retardation corresponding to one-quarter of the wavelength of the incident light due to the polarization beam splitter plus the retardations due to the color separating and synthesizing means, it is possible to reduce by that amount the leakage of the optical image component, which originally should not be emitted from the polarization beam splitter to the projection optical system, to the projection optical system side and thereby possible to prevent a reduction of the contrast due to the haze phenomenon.
Further, by arranging phase difference plates for doubly refracting the incident light and the optical images and setting retardations at the phase difference plates based on the results of the ray tracing from the polarization beam splitter to the reflection-type image forming means, changing in accordance with the characteristics of the color separating and synthesizing means with respect to the angle of incidence and wavelength, it is possible to take into consideration the characteristics of the color separating and synthesizing means and reduce the leakage of the optical image components to the projection optical system side and thereby possible to prevent a reduction of the contrast due to the haze phenomenon.
Further, according to the third, fourth, and fifth aspects of the present invention, by arranging phase difference plates for doubly refracting the incident light and the optical images at the refraction-type image forming means, it is possible to use the phase differences given to the incident light and optical images at the phase difference plates to reduce the polarization component causing the occurrence of the haze phenomenon. At this time, by rotating the phase difference plates in planes substantially orthogonal to the optical axes so as to adjust the phase differences given to the incident light and the optical images, even when the reflection-type image forming means etc. are arranged at an inclination, it is possible to prevent an increase in the polarization component causing the occurrence of the haze phenomenon due to the inclination. Therefore, it is possible to prevent the reduction of the contrast due to the haze phenomenon reliably due to the that much simpler assembly precision.